Whitespace and semi-colon cleanup.

Leave Ruby files with two space indents only; everything else as
tabs only (most files had a bit of both). Semi-colons: add
missing ones and remove redundant ones.
Update to latest compatible gems.
Update OpenPGP.js to version 0.9.0.

Refactor to use new Promises-based OpenPGP.js API introduced in
OpenPGP.js version 0.8.0. Include a polyfill for ES6-style
Promises: https://github.com/jakearchibald/es6-promise
Update Pure CSS to version 0.5.0.